Optical Arbitrary Waveform Generation (O-AWG) is a promising technology for generating high-bandwidth analog microwaves used in advanced radar systems and ultra-wideband communications systems. O-AWG utilizes waveform generation and shaping in the optical domain to overcome the speed limitation of electronics. By “arbitrary” is meant that any waveform of interest may be generated. The ability to dynamically change the waveforms in the field is of particular interest because it allows higher degree of freedom for optimization and control.
Techniques for dynamic pulse shaping in the optical domain can be generally divided into two categories: direct temporal shaping (such as that described in: Capmany et al., Journal of Lightwave Technology, 13, pp. 2003, 1995; Shen et al., IEEE Photonics Technology Letter, 16, pp. 1155, 2004) and temporal shaping through spectral manipulation (such as that described in: Weiner, Review of Scientific Instruments 71, 1929, 2000; Azana et al., Optics Letters 30, pp. 3228, 2005; Kaplin et al., in Ultrafast Optics IV: Selected Contributions to the 4th International Conference on Ultrafast Optics (Springer, 2004), pp. 105-118). The former utilizes multiple delays in time to sample and then manipulate the optical signal in time domain. The latter case typically uses free-space diffraction gratings (as described in Weiner), arrayed waveguide gratings (as described in: Yilmaz et al., IEEE Photonics Technology Letter, 14, pp. 1608, 2002), Fiber Bragg Gratings (as described in: Brennan III et al., U.S. Pat. No. 6,195,484), or dispersive fiber (as described in Azana et al.) to separate the frequency contents of a signal, and then use a Spatial Light Modulator (SLM) (as described in Weiner) or an Electro-optic Modulator (EOM) (as described in: Azana et al.; Brennan III et al.) to manipulate the spectral content of the signal. All these techniques, however, requires the light signal to couple out of fiber for spectral manipulation and then couple back into the fiber—the inherent loss is therefore high.
It would be desirable to provide a method for dynamic waveform shaping that addresses at least some of the above concerns.